R/V Fast Eddy on Medicine Lake

R/V Fast Eddy tied
up to a pier on Medicine Lake. Commonly used for research on San
Francisco Bay, Fast Eddy can be transported by trailer from its home
at the USGS Marine Facility (Marfac) in Redwood City, CA, to more
distant field locations. Prior to the work in Medicine Lake, it
was outfitted with a new system for collecting high-resolution
profile data and a canvas covering to protect instruments and
operators from the hot sun.

Last September, Larry Phillips, Pat Hart, Larry Kooker, Gerry O'Brien,
and Jon Childs completed a geophysical survey and sampling program of
Medicine Lake using the newly outfitted R/V Fast Eddy. Jake Lowenstern
of the Volcano Hazards Team (VHZ) organized the survey effort. The
field party included John Barron and Scott Starratt of Climate
Change (VHZ) and Jim Rytuba of Western Mineral Resources.

Medicine Lake, located in Siskiyou County in northern California, sits at an
elevation of about 7,000 ft, within the ancient caldera of the
Medicine Lake volcano complex. Medicine Lake volcano is a Pleistocene
and Holocene shield volcano located in the Cascade Range, 50 km
northeast of Mount Shasta. Medicine Lake volcano lavas cover about
2,000 km2, and the total volume of
the volcano is estimated at 600 km³,
larger than Mount Shasta, which
is the largest of the Cascade stratocones. The most recent Medicine
Lake volcano eruption occurred about 0.9 ka. At least 17 eruptions
have occurred since 12 ka, or between one and two eruptions per
century on average. More information is available
online.

Detailed bathymetric and geopulse-reflection profile data were acquired
along with surface-water temperature and temperature-depth profiles.
The reflection data were particularly interesting, revealing structure
to 40 m and more beneath the lake bottom. The lake ‹sedimentsŠ proved,
unfortunately, relatively impenetrable to the small hand-coring
instruments available, and further investigation will have to await
a vibracoring effort planned for next year. Once the lake sediments
are sampled, USGS researchers hope to use them to unravel the volcanic
and climate history of the region and the geochemical behavior of
mercury in volcanic terrains.

Medicine Lake is a popular camping and fishing spot, and considerable
public interest has been expressed in a new bathymetric map to replace
the old one that dates back to 1955. Using the bathymetric data
collected last September, we have just completed such a map, soon
to be published.